Method of generating gear-teeth



C. H. SCHURR.

METHOD 0F GENERATING GEAR TEETH.

APPLICATlON FILED NOV. l2, |914. v 1,355,919. Patented 00t.1 9,1920.

( 3 SHEE] S-SHEET I C. H. SCHURR.

METHOD 0F GENERATING GEAR TEETH.

APPLICATION FIL-ED Nov. l2, 1914.

Patentedv Oct. 1920.

3 SHEETS- T 2.

. CHURR- METHD 0 ATING GEAR TEETH.

APPLICA ED Nov. 12. 1914.

' Patented 0013.19, 1920.

3 sHEETs-sHEET 3.

UNITED STAT 1:S

PATENT OFFICE.

CHARLES H. SCHURR, 0F CLEVELAND, OHIO, ASSIGNOR TO THE LEES BMDNER COMPANY, OF CLEVELAND, OHIO.

METHOD 0F GENERATING- GEAR-TEETI-.

Specification of Letters Patent.

Patented Oct. 19, 1920.

riginal application filed .Tuly 9, 1914, Serial No. 849,955. Divided and this application led November 12, 1914. Serial No. 871,805.

To all whom t may concern.'

Be it known that I, CHARLES H. SCHURR, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented a new and useful Improvement in Methods of Generating Gear-Teeth, of which the following is a specification, the principle of the invention being hereinexplained and the best mode in which I have contemplated applying that principle, so as to distinguish it from other inventions.

This invention constitutes Subject matter divided out frommy pending application filed July '9, 191.4, Serial No.y 849,955. The method herein explained involves the superior generating as contra-distinguished from the old form cutter or templet system whereby gears provided with teeth having faces conforming to a curved Surface may be produced from a single integral blank. I employ a special milling machine illustrated diagrammatically in Figure I.

My object has been to manufacture mating gears the curved faces of which may be cut with such interrelated accuracy that when they are rolled together a working contact can be had entirely thereacross. In this manner the driving of one by the other is continuous and hence smoother. y

It may be well to distinguish between the product of my method and what is generally known as a gear of the herringbone type. (1) my method completes a gear from an integral blank, while the herringbone requires that complementary parts be finished separately. (2) The faces of my product must conform to a resultant curve whereas a herringbone is merely a combination of right and left hand helical gears. (3) My cutter describes a curve not convolved'about the axis of the blank and the cutter is furthermore the base of the system... Any number 'fof teeth finished after the manner of my invention are interchangeable with another gear which was cut by the same or conjugate cutter though having a dier'ent number of teeth..

The inventive conception is associated with mechanism for practising my method which method is hereina fter explained and variously combined in the claims. While the annexed j drawings and particular description thereof,

modified forms based upon my invention, it should be understood that such mechanism only exemplifies one of many diversified mechanlcal agencies by which the principle of my invention may be properly carried out.

Adverting to the drawings: Fig. I is a diagrammatic view of a milllng machine capable of carrying out my improved method.

Fig. II is viewed on line II-II of Fig. I showing a plan view of the edge of a partially completed blank, and path of the cutter in dotted lines.

Fig. III is an enlarged edge elevation of a gear showing a limited series of teeth finished according to my method and with the relative adjustment of parts as shown in Fig. I.

Fig. IV is a section on line IV-IV of Fig. III..- j

Fig. V is a vsimilar' view 4to Fig. II aftef' readjustment.

Fig. VI is an enlarged view similar to that seen in Fig. III involving a modified form of tooth outline based on the arrangement of thereof.

Fi X is a similarly enlarged view as Fig. 1 III of a mating gear showing spaces and teeth interchanged.

Fig. XI is a-section on line XI-XI of roceeding first to the description of the essential elements of the machine outlined. In Fig. I will be seen a bed A upon which the carriage B is adapted to travel. The n carriage mounts a rotatable spindle C which carries a segment D to serve as a form or base circle. A fixed rack E is intended to coperate with the segment and constituteone exemplifying guiding means. In operative proximity is a tool supported in any suitable manner for operation upon the gear blank Gr, likewise carried on the spin-- l dle C. A driving shaft 1 transmits its power to effectin turn the rotation of shaft 2 in the'direction indicated by the arrow, Ithe crate the long-faced pinion 2a, and the large gear 3 Ywhich -is keyed to a sleeve 4 in which the cutter T is mounted. In the exemplification selected a hollow faced end mill appears having its axis perpendicular both to the spindle C or axis of the blank and to the prescribed direction of travel of the carriage. Simultaneously power is transmitted from the driving shaft l to a shaft 5 thence to a pair of pinions 6 one of which meshes directly with a gear 7 provided with jaw teeth while the other meshes indirectly with a similar gear 7 and directly with an idler 8. The gears 7.are mounted upon the same shaft 9 such that one or the other may be brought in connection with a clutch 10 manually controlled at l1. In this manner the direction of rotation of the traversing screw 12 may be altered at will. y

In operation the cutter is presented'in working proximity to some particular tooth and rotated while the blank is simultaneously caused to traverse, and be rolled along, through a predetermined arc. Thereafter the cutter continues in the same direction while the direction of rotation of the blank is automatically reversed through the agency of the guiding means coincident with a re versal of the traverse. VUpon the completion of the cut upon one tooththe blank is properly indexed (rotated) in any approved manner not necessary to be shown since common in the art;

It will be apparent from an inspection of Fig. II that the revolution of the mill, together with the simultaneous movement of the blank serves to generate a tooth having faces curved according to the resultant of the combination of movements. 'Looking next to Fig. III it will be noticed that each tooth g on the blank is of concavo-convex form to present different faces g2 and g3. In this form the cutting engagement is.L a wholly receding one across'the entire thickness of the gear beginning at one side as shown in Fig. II. In this case the cutter assumes its extreme or most advanced position at the moment it engages'the side edge ofthe blank. Any two adjacent teeth faces are generated with a different radius from a common center, and as a necessary manufacturing incident, with the result that the shape and size of the finished teeth do not correspond to that of the intervening spaces.

The purpose in rolling the blank G along.

with relation to the cutting edge of the tool" T is to secure the full depth of cut and genproper tooth profile. While it is quite possible moreover togfeed the cutting tool, it is not absolutely necessary because a cut of full depth may be made, and this latter mode is followed in the drawings as particularly shown in Fig. I.

The modification seen in Figs. VI and VII involves a change in that the curved faces of the number'of teeth.

g4 and g5 have a uniform approach toward and recession from the `median annular plane. In operation the rotation of the cutter is not a continuous recession across the entire thickness of the blank as was explained in reference to Fig. II, but an advance across the first thickness of the blank and a recession across the other half as shown in Fig. V. If for example the blank in Fig. I were shown cut on the median plane, the most advanced cutting edge or the one farthest to the left (in the position it is momentarily seen to occupy in Fig. I) would be just crossing the median plane of the blank preparatory to beginning its recessional traverse across the thickness of the blank. Therefore the type of teeth seen in Fig. VI would be theresult.

Figs. VIII and X represent novel mating gears capable of being produced by my method so as to be absolutely accurate and reliable. As/a matter of clearness the teeth in each of these gears are designated, t, and t', and the intervening spaces, s, and s', respectively. The feature of these gears is pronounced by the fact that the teeth of either one correspond with the spaces of the other, though not with its own spaces. In Fig. VIII, the opposite faces g and g7 of any one tooth are of different curvature and likewise the opposed faces of adjacent teeth. l So, also, in Fig. X, the opposite faces g8 and 99 of the teeth are of distinct curvature and the opposed faces of two adjacent teeth are of different curvature, but correspond precisely with opposite faces respectively of any particular tooth in Fig. VIII. The two gears shown in Figs. VIII and X effect a true generative roll across the entire width and in a manner so far as I am aware, quite unique. v

This invention involving a generating action as contradistinguished from a forming action, it may be well to define the difference.

A generating action. involves a movement of both blank and tool so that the cut is a resultant of a combination of movements. A forming action is such that the tool effects an absolute reproduction of the path of movement of its cutting edge. A spur gear manufactured according to this method has its root diameter of cylindrical outline, or in other words, its teeth are of equal depth from side to side. Vhile the tool employed to produce it has a pair of cutting edges which describe concentric paths, such'edges simultaneously cut concentric arcuate elements. An advantage of employing a generating scheme for simultaneously cutting adjacent tooth faces is that it may be practicable upon large and small gears so that they are always interchangeable regardless It is apparent from an inspection of Figs. VIII and X that the conjugate partially completed gears are adapted to be rolled together and to be interchangeable irrespective of size because based on the same system, indeed, they are each capable of rolling along a-rack which is a gear of infinite radius and which may be considered as the base of the system .or a developed plan of'theperiphery of the gear which is conjugate to the one which is to be rolled along such rack. In other words, the rack corresponding to the developed plan of say, the gear shown in Fig. VIII will be truly conjugate to the teeth about the periphery of the gear shown in Fig. X. The tooth spaces s in Fig. VIII are conjugate to the teeth t in'Fig.,X and the spaces s in Fio'. X are conjugate to the teeth t in Fig. VI I. Moreover, since two adjacent tooth faces are simultaneously generated with a different radius from a coinmon center the spaces s shown in Fig. V III are defined by opposed tooth faces which are simultaneously cut by the employment of a male cutter whereas the teeth t in Fig. X have opposite faces produced by a female cutter which straddles the tooth. The cutting edges of the male cutter correspond therefore with the cutting edges of the fe` male cutter. In each case, while the distance between the defining faces of the spaces and the thickness of the teeth is not uniform when measured in planes parallel to the sides of the gear blanks they are the same in Figs. VIIIand X, respectively, if measured radially with reference to the center of the cutter. Since the spaces s are conjugate to the teeth t and the spacesjs are conjugate to the teeth t they are necessarily also complemental to a pair of base racks or gears of infinite radius. The cutting edges of either the male or female tool correspond precisely to the sides of a base rack tooth.

My invention being thus described with sufficient thoroughness, what I desire to secure by Letters Patent and therefore claim specifically, is:

l. The method of generating the teeth of gearing of the character referred to, by means of a pair` of cutting edges moved along a circular path in a plane parallel to the axis of the blank in order simultaneously to cut adjacent tooth faces, which consists i-n producing relative movement between the cutting-edges and the gear bl anke in a direction at right angles to the axis of the blank during the movement of the cutting edges through the blank from one side thereof to the other, indexing the blank, and repeating the cutting of a distinct pair of adjacent tooth faces lso that any particular face is composed of arcuate elements which are concentric with reference to arcuate elements of its one adjacent face and eccentric with reference to arcuate elements Aof 'the other adjacent face.

. arcuate elements '2. The method of generating the teeth of gearing of the character referred to by simultaneously cutting adjacent tooth faces, which consists in moving a pair of cutting edges along a circular path in a `plane parallel to theaxis of the blank producing a distinct relative movement between the cutting edges and the gear blank to effect a generating engagement, indexing the blank, and repeating the simultaneous cutting of a distinct pair of adjacent tooth faces so that4 any particular tooth face is composed o arcuate elements which are concentric with reference to arcuate elements of the nearest tooth face in one direction around the gear and eccentric with reference to of the nearest tooth face in the opposite direction around the gear.

3. The method of generating gear teeth which consists in simultaneously revolving across the periphery of the blank two cutting edges having the relation to each other of lateral edges of rack teeth which are conjugate to the tooth spaces of the gear which it is intended to produce, simultaneously rotating such blank about its own axis and effecting a straight line traverse thereof perpendicularly to its own axis wherebyv alternate pairs of,- finished tooth faces assume different relationships relative to eachother respectively.

4. The method of generating gear teeth which consists in simultaneously rotating a blank, revolving a pair of cutting edges and effecting an additional straight line movement of one of the engageable parts perpendicularly to the axis of the blank so as to effect a generating engagement; whereby simultaneously to cut spaceddefining faces along arcs of movement having la common center though. necessarily different radius and in consequence form teeth intervening spaces of equal normal breadth measured in a direction from one side of the gear to the other but different breadth measured parallel to the -median plane of all the spaces. j,

, 5. The method of simultaneously finishing a pair of spur gear teeth faces to final involute profile which consists in bringing a blank and a multiple edged cutter into generating engagement with each other, causing the cutter simultaneously to cut from a pair of tooth faces upon the blank along two concentric lines which intersect the pitch line of the gear blank, indexing, and repeating the cutting operation upon a distinct though next adjacent pair of'faces whereby to establish an alternate or intermediate pair of tooth faces which include -eccentric lines intersecting the pitch line` taneously effecting a pair of nishing cuts from space defining faces of ya gear blank by relative action of one kind between the operative parts while simultaneously imparting a distinct relative generating action therebetween, and eil'ecting a pair of cuts in like manner from a distinct next adjacent pair of space defining faces.

7. The method of producing conjugate gears having curved teeth of varying normal thickness, which consists in imparting partial rotation to a blank, causing a cutting edge to travel with a given radius around a center in operative engagement with a blank while simultaneously effecting a generating relative movement between said blank and cutter and causing a second cutting edge to travel in operative engagement around the same center with a different radius, such pair of cuts being made upon an adjacent pair of faces, indexing the blank, and repeating the same double cutting operation upon two adjacent faces each of which is distinct.

8. The method of producing conjugate gears having curved teeth spaced apart uniform normal distances, which consists in turning a blank, causing a cutting edge to travel with a given radius in operative generating engagement with the bla-nk while simultaneously effecting relative movement between said blank and cutter, causing another cut-ting edge to travel in operative engagement with a different tooth face of the blank around the same cent'er with a different radius, such cuts producing space defining faces, indexing, and again causing cutting edges with different radii to travel around a center in operative engagement with said blank to produce a second pair of Ispace defining faces while simultaneously effecting a generating relative movement between said blank and cutter.

9. The method of generating gear teeth which consists in simultaneously revolving across the periphery of the blank two cutting edges having the relation to each other of two lateral tooth edges of a rack which are conjugate to the gear which it is intended to produce, simultaneously rotating such blank about its own axis and effecting between it and the tool a relative straight line traverse whereby alternate pairs of finished tooth faces assume different-relationships relative to each other respectively.

Signed by me, this 4th day of November, 1914.

CHARLES H. SCHURR.

Attested by- MARIE WAGNER, C. F. FRANKE. 

